In a constant search for increased production, the textile industry in very recent times has heavily focussed on the use of looms for weaving fabric in which the filling or weft yarn is inserted by means of a flowing stream of a pressurized fluid, such as air or water. Such looms eliminate the necessity for a mechanical shuttle as the vehicle for projecting the weft yarn during weaving together with the mechanical driving mechanisms necessitated by a shuttle, and consequently offer inherent advantages from the standpoint of increased operation, simplified mechanical construction, and decreased operating noise, all of which are significantly desirable.
In a conventional shuttle operated loom, all of its elements are mechanically interrelated to the operation of a crankshaft and, consequently, the synchronization of the timing of the various significant events which transpire during each weaving cycle can be readily coordinated and adjusted relative to the rotation of the crankshaft. In a loom where the filling is propelled by a pressurized fluid stream, however, all of the significant operating events need no longer be directly related to crankshaft rotation and consequently it becomes more difficult to insure that the timing of these events is brought into the precise synchronism required for high speed operation.
Furthermore, where some of the instrumentalities employed in fluid weft insertion looms are operating independently of the crankshaft, when defective operation does occur, as will necessarily happen occasionally, it is considerably more difficult to trace the cause of a particular defective pick than was the case with conventional mechanically engineered looms.
It will be apparent that the introduction of pressurized fluid to the weft propulsion nozzle of the fluid weft insertion loom is the primordial event in the cycle of operation of that loom. That is to say, until the pressurized fluid has been delivered to the weft propulsion nozzle, the delivery of the length of weft across the shed of a loom remains an impossibility. Hence, all subsequent events in the successful completion of the loom operating cycle depend upon nozzle pressurization as the initiating event and in the absence of successful completion of this initiating event, all other events become irrelevant and indeed nonexistent. Consequently, it is important in controlling the operation of the loom operating cycle to be able to precisely identify the occurrence as well as the instantaneous timing of the occurrence of nozzle pressurization, and the development of means for accomplishing this objective would be a useful advance in this field.